Machine and Method for the Production of a Web of Fiber Material with an Increased Volume

ABSTRACT

A machine for the production of a web of paper or other fiber material ( 1, 6, 17, 37 ), comprising a belt ( 14, 26, 43 ), wherein the length of the belt ( 14, 26, 43 ) is elastically extendable, the web of fiber material ( 1, 6, 17, 37 ) can be fed to the belt ( 14, 26, 43 ) when the belt ( 14, 26, 43 ) is in extended state and the belt ( 14, 26, 43 ) can be slackened when the web of fiber material ( 1, 6, 17, 37 ) is placed thereon, such that the web of fiber material ( 1, 6, 17, 37 ) is compressed and the adhesion forces between the web of fiber material ( 1, 6, 17, 37 ) and the belt ( 14, 26, 43 ) are sufficiently high in order to avoid the formation of folds in the compressed web ( 1, 6, 17, 37 ).

The invention relates to a machine for producing a fibrous web of paperor some other material.

A pressing section for a paper machine is known from DE 100 22 087 A1.The pressing section comprises two pressing units, each of which isformed from a press roller working in association with a shoe pressroll. A first upper felt runs through the first pressing stationtogether with a paper web passing forward from a forming fabric, anunder-felt and a press jacket of a first shoe press roll. Together withthe under-felt, the paper web passes on to the second pressing station.Then the paper web together with a second upper-felt and a press jacketof a second pressing station runs through the second pressing station.The paper web continues to follow the under-felt to a pick-up roll bymeans of which it is transferred to a first drying fabric which conveysthe paper web to the drying section. Deflection rolls and suction rollsare provided to deflect the upper-felt and the lower-felt. In the caseof pressing sections known from the state of the art the very lowstrength of the paper web makes it necessary to provide continuoussupport by felts or a transfer belt.

Particularly in the case of wood-free papers for office use such ascopying or printing paper, the volume of the paper for a given degree ofsmoothness—which when determined by the Bendtsen method amounts to lessthan 200 ml/min—constitutes a quality feature, the maintenance of whichgives rise to problems on fast-running paper machines and highdry-weight contents. The requirement for high dry-weight contents afterpassing through the pressing section which is made necessary by theincrease in the running speeds leads to an undesired reduction in thespecific volume of the paper.

It is the object of the invention to create a machine in which thevolume of the fibrous web is increased without the need to accept alower dry-weight content than can be attained within the state of theart.

According to the invention this object can be achieved with a machine ofthe type initially mentioned by providing a belt which is elasticallyextensible longitudinally, it being possible for the fibrous web to beled to the belt in its elongated condition after which the belt with thesuperimposed fibrous web can be relaxed so that the fibrous web iscompressed and the adhesive forces between the fibrous web and the beltbeing sufficiently great that fold formation in the compressed fibrousweb is prevented.

According to the invention an infinitesimal compression of the paper webis achieved on the support material on which it is carried. The paperweb is first transported on a felt and then transferred to an elasticbelt, i.e. a fabric. a felt or a transfer belt which is under tension.The tensioned belt is relaxed with the result that compression of thepaper web takes place. The belt is advantageously of such a nature thatthe high adhesion forces which exist between the fibrous web and thebelt prevent fold formation in the paper web and ensure an infinitesimaldegree of compression.

An increase in volume can be obtained from the infinitesimal compressionof the paper web without a linear increase of substance in relation tothe gain in volume. A particular advantage of the invention consists,therefore, of an increase in volume without a superproportional increasein substance.

Advantageous further developments of the invention are described in thesubsidiary claims, the description and the drawings.

In an advantageous manner, the elongation and relaxation of the belt arecombined with an intermediate de-watering stage. The de-watering cantake place at different points of the machine, for example, in thepressing section or the drying section. This manner of processingachieves a particularly high gain in volume.

If the machine possesses at least one pressing section with severalpress-nips it is advantageous if the belt can be elongated in front ofor during its passage through the first press-nip and relaxed afterpassing through the last press-nip, with the fibrous web and the beltbeing led together in front of or within the first press-nip. In thisway the belt is, therefore, elongated before or in the first press-nipand the fibrous web is de-watered once or several times as it passesthrough press-nips, after which the belt is again relaxed.

If the machine possesses at least one pressing section with one or morepress-nips it is conceivable to elongate the belt in front of itspassage through a press-nip, to release the tension after passingthrough the same press-nip and to bring the fibrous web and the belttogether in front of or within the press-nip.

It should be noted here that the elongation and relaxation of the beltcan be achieved by two possible mechanisms:

1. Tensioning the belt in advance of the nip by a higher speed relativeto the nip together with reducing the speed after the nip.

2. The belt is so flexible in its thickness that when it is exposed topressure in the nip the reduction in its thickness is associated with alengthening of the belt. Relaxation of the belt leads not only toexpansion in the thickness direction but to a reduction in length and aresulting compression of the belt and of the fibrous web adhering to it.

Advantageously, with the aid of a suitable tilt it is possible for theprocesses within the nip to proceed in a controlled manner.

In an advantageous configuration of the invention a deflection roll isprovided before the at least one press-nip and this can be driven at alower speed than the first and second press-rollers which together formthe press-nip through which both the fibrous web and the belt are fed.The difference in speed between the press rollers on the one hand andthe deflection roll mounted immediately ahead of them arises from thefact that relative to the deflection roll the press rollers are drivenat a higher speed.

In order then to compress the fibrous web, a deflection roll after theat least one press-nip is provided which is driven at a lower speed thanthe first and second press rollers.

In an advantageous configuration of the invention, the second belt is atransport belt to transfer the fibrous web to a third belt by means ofwhich the fibrous web can be led through a third press-nip to improvethe level of smoothness.

Alternatively, the second belt is a transport belt to transfer thefibrous web to a third belt by means of which the fibrous web can be ledthrough a drying section following the pressing section.

The invention also relates to a process for operating a machine for theproduction of a fibrous web of paper or some other material by thefollowing steps:

the elongation of a belt length-wise

the forward movement of a fibrous web on the belt in its elongatedcondition

the relaxation of the belt so that the fibrous web is compressed and

ensuring that the adhesive forces between the fibrous web and the beltare sufficiently high that fold formation in the compressed fibrous webis avoided.

In an advantageous further development the process for operating themachine is characterized in that when the fibrous web is transferredfrom the belt, for example, to improve its level of smoothness, it ispressed against a succeeding transport belt.

It is of advantage if the fibrous web is compressed by less than 5% and,in particular, by less than 3%.

There follows a more detailed explanation of the invention with the aidof exemplary embodiments.

FIG. 1 a, b show schematic sectional elevations of the fibrous webbefore and after being compressed,

FIG. 2 shows a fibrous web, which is fed through a press nip,

FIG. 3 shows a pressing section with a central roller forming twopress-nips,

FIG. 4 shows a pressing section with a central roller forming twopress-nips combined with a part of the drying section and

FIG. 5 shows a pressing section with two press-nips, each of whichcomprises individual pairs of press rollers where the second press-nipis formed of a press roller with a shoe press roll.

A fibrous web 1 (FIG. 1 a) passing forward from a forming section is ledthrough a pressing section. There, it is led through at least onepress-nip. The fibrous web 1 is deposited upon an elastic belt 2 whichfinds itself in an elongated condition before it passes through thepress-nip. After the press-nip, the elongation of the belt 2 is relaxedby, for example, running a deflection roll following the press rollersat a lower peripheral speed relative to the running direction of theweb. In this way the fibrous web 1 is compressed. Instead of theoriginal thickness d it has the thickness D (FIG. 1 b).

FIG. 2 shows schematically a press-nip comprising a press roller 3 and apress-shoe (not illustrated) through which the fibrous web 1 is ledtogether with two belts or felts 4, 5.

In a configuration of the invention a fibrous web 6 (FIG. 3) is receivedon a felt 54 from a forming section 7 and led to the pressing section 8.Here it is first led through a press-nip 51 comprising rolls 10 and 50and then through two press-nips 12, 13 comprising a central roll 9 withtwo press rollers 10, 11.

The fibrous web 6 is led through the press-nip 51 together with the felt54 and an elastic belt. In this way the elastic belt 14 is first ledthrough the press-nip 51. The belt 14 is not elongated ahead of thepress-nip 51 but, on the contrary, within the press-nip 51 itself as aconsequence of the pressure loading. In this respect, the belt 14 is soflexible in its thickness that when subjected to pressure loading withinthe press-nip 51 the reduction in thickness is associated with alengthening of the belt 14. The relaxation of the belt 14 after itspassage through the press-nip 51 leads not only to an increase inthickness but also to a reduction in length and an associatedcompression of the belt 14 and the fibrous web 6 adhering to it. Thenthe fibrous web 6 passes through the press-nips 12, 13 formed by thecentral roll 9 and the rolls 10 and 11.

In another embodiment (FIG. 4) a fibrous web 17 travelling from aforming section on an under-felt 18 is led to a pressing section 19 witha central roll 20. This forms two press-nips 21, 22 with the pressrollers 23, 24 of which the press roller 23 is simultaneously designedas a suction roll in order to release the fibrous web 17 from theunder-felt 18. Before the first press-nip 21 an application of, forexample, starch carried on an air-permeable belt 26 is made by a device25. This belt together with the fibrous web 17 transported upon it isheated and dried by drying devices 27, 28 with heating applied to bothsides or at least to one side and, in particular, to the upper side. Theupper drying device 28 produces hot air while the lower drying device 27is, for example, a radiant dryer. In addition, a further drying device29 for the fibrous web 17 can be arranged in the following area of adrying fabric. To provide for the situation that the belt 26 ispermeable to air, both drying devices 27, 28 are radiant dryers.However, the use of an air-permeable belt 26 has the advantage thatdrying can take place through it.

A conditioning device 30 is fitted to the belt 26. For example, acleaning agent can be applied by spraying which is subsequently removedby wiping.

In the press-nip 21, the belt 26 transfers the application of the mediummade by the device 25 to the fibrous web 17 while it, together with thefibrous web 17, is wrapped around the central roll 20.

Furthermore, the belt 26 is of an elastic nature so that firstly it iselongated by a deflection roll 31 turning at a lower speed than thecentral roll 20 and the press rollers 23, 24 and it accepts the fibrousweb 17 while in this elongated condition. After passing through thepress-nips 21, 22 the belt 26 is again compressed by a slower-runningdeflection roll 32 with similar compression of the fibrous web 17carried upon it, which as a result simultaneously is endowed with agreater thickness and, thereby, a greater volume.

After passing through the pressing section 19 the fibrous web 17 is ledinto a single row drying section 33 with drying cylinders 34 anddeflection rolls 35 in the form of suction rolls together withlow-pressure areas 36. In these a pressure reduction of preferably morethan 5 kPa is maintained to facilitate a reliable release of the fibrousweb 17 from the drying cylinders 34 because the side of the fibrous web17 carrying the medium lies upon the peripheral face of the dryingcylinders 35.

In a further exemplary embodiment (FIG. 5) a fibrous web 37 isde-watered by press-nips 39, 40 in a pressing section 38. The firstpress-nip 39 is formed by the pair of rolls 52 and 53. In the secondpress-nip 40 the fibrous web 37 is led between a press roller 41 and ashoe press roll 42. At the same time moisture is given up to an elasticfelt 43. The latter is led over deflection rolls 44, 45, 46, 47. Each ofthe deflection rolls 44, 47 are designed as driven rolls. The deflectionroll 44 runs at a slightly slower peripheral speed than the press roller41 and the shoe press roll 42 with the result that the felt 43 iselongated when it receives the fibrous web 37 from an upper felt 48before reaching the press-nip 40.

After passing through the press-nip 40 the felt 43 and the fibrous web37 carried by it is compressed because the deflection roll 47 turns witha slightly lower peripheral speed than the press roller 41 and the shoepress roll 42. The fibrous web 37 is led by the felt 43 to a dryingsection 49.

1. A machine for producing a fibrous web of paper or some other material(1, 6, 7, 37) with a belt (14, 26, 43), characterized in that the belt(14, 26, 43) is elastically extensible longitudinally, it being possiblefor the fibrous web (1, 6, 17, 37) to be led to the belt (14, 26, 43) inits elongated condition after which the belt (14, 26, 43) with thesuperimposed fibrous web (1, 6, 17, 37) can be relaxed so that thefibrous web (1, 6, 17, 37) is compressed and the adhesive forces betweenthe fibrous web (1, 6, 17, 37) and the belt (14, 26, 43) beingsufficiently great that fold formation in the compressed fibrous web (1,6, 17, 37) is prevented.
 2. The machine as claimed in claim 1,characterized in that the machine comprises at least one pressingsection (8, 19, 38) with at least one press-nip (12, 13, 21, 22, 39, 40,51) and that the belt (14, 26, 43) can be elongated in front of orduring its passage through the first press-nip (21) and relaxed afterpassing through the last press-nip (22) and that the fibrous web (1, 6,17, 37) and the belt (14, 26, 43) can be led together in front of orwithin the first press-nip (21).
 3. The machine as claimed in claim 1,characterized in that the machine comprises at least one pressingsection (8, 19, 38) with at least one press-nip (12, 13, 21, 22, 39, 40)and that the belt (14, 26, 43) can be elongated in front of or duringits passage through a press-nip (40, 51) and relaxed after passingthrough the same press-nip (40, 51) and that the fibrous web (1, 6, 17,37) and the belt (14, 26, 43) can be led together in front of or withinthe press-nip (40, 51).
 4. The machine as claimed in claim 1,characterized in that a deflection roll (31, 44) is provided before theat least one press-nip (21, 22, 40) and this can be driven at a lowerspeed than the first press roller (23, 41) and the second press roller(20, 42).
 5. The machine as claimed in claim 1, characterized in that adeflection roll (32, 47) is provided after the at least one press-nip(21, 22, 40) and this can be driven at a lower speed than the firstpress roller (23, 41) and the second press roller (20, 42).
 6. Themachine as claimed in claim 1, characterized in that after passingthrough the press-nip (12, 13, 21, 22, 39, 40, 51) the fibrous web (1,6, 17, 37) led forward together with a belt can be transferred to asecond belt running at a lower speed relative to the belt.
 7. Themachine as claimed in claim 6, characterized in that the second belt isa transport belt to transfer the fibrous web (1, 6, 17, 37) to a thirdbelt by means of which the fibrous web (1, 6, 17, 37) is led through athird press-nip.
 8. The machine as claimed in claim 6, characterized inthat the second belt is a transport belt to transfer the fibrous web (1,6, 17, 37) to a third belt by means of which the fibrous web (1, 6, 17,37) can be led through a drying section following the pressing section.9. The machine as claimed in claim 1, characterized in that the belt(14, 26, 43) is a fabric, a felt or a transfer belt or a smoothing belt.10. A process for the production of a fibrous web of paper or some othermaterial (1, 6, 17, 37) having the following steps: the elongation of abelt (14, 26, 43) length-wise the forward movement of a fibrous web (1,6, 17, 37) on the belt (14, 26, 43) in its elongated condition therelaxation of the belt (14, 26, 43) so that the fibrous web (1, 6, 17,37) is compressed and ensuring that the adhesive forces between thefibrous web (1, 6, 17, 37) and the belt (14, 26, 43) are sufficientlyhigh that fold formation in the compressed fibrous web (1, 6, 17, 37) isavoided.
 11. A process for operating a machine as claimed in claim 10,characterized in that in order to smooth the fibrous web (1, 6, 17, 37)when it is transferred from the belt (14, 26, 43) the web is pressedagainst a succeeding transport belt.
 12. The process as claimed in claim10, characterized in that the fibrous web (1, 6, 17, 37) is compressedby less than 5%.
 13. The process as claimed in claim 10, characterizedin that the fibrous web (1, 6, 17, 37) is led forward with a dry-weightcontent of less than 60%.
 14. The process as claimed in claim 10,characterized in that the fibrous web (1, 6, 17, 37) is compressed byless than 3%.
 15. The process as claimed in claim 10, characterized inthat the fibrous web (1, 6, 17, 37) is led forward with a dry-weightcontent of less than 40%.